The present invention relates to a system for controlling an electromagnetic clutch for a vehicle having an infinitely variable belt-drive automatic transmission.
U.S. Pat. No. 4,401,199 discloses a system for controlling an electromagnetic clutch of an internal combustion engine mounted on a vehicle, in accordance with the engine speed and vehicle speed. Further, U.S. Pat. No. 4,369,675 discloses an infinitely variable belt-drive transmission for a vehicle. The transmission comprises an endless belt running over a driving pulley and a driven pulley, each pulley being so designed that the running diameter of the driving belt on the pulleys varies by a hydraulic control system. In the system, operational ranges such as a drive range (D range) and reverse range (R range) are provided. In addition, it has proposed to provide a high engine speed drive range (Ds range) in the infinitely variable belt-drive transmission. When the Ds range is selected while driving in the drive range, the transmission ratio is increased, so that increased speed of the engine to drive the vehicle can provide an active drive of the vehicle. In other words, the vehicle is driven in a high engine speed range. However, since the transmission ratio is increased in the Ds range, engine speed must be rapidly increased in order to keep the vehicle speed constant. Accordingly, if the engine speed is not rapidly or sufficiently increased to meet the downshifted transmission ratio, the vehicle speed is greatly decreased by the engine braking effect, which will cause a great shock.